I absolutely love the build quality...it makes me smile just holding it. Aside from that, the viewfinder is amazing, Autofocus is exceptional, and image quality seems much better than my 20D. The menu does take getting used to if you are new to a 1D, but I like them now.

Cons:

Leanring curve. I think I had unrealistic expectations of the AF. Can the thing just be water proof?

Sometimes I wish it would focus quicker in low light, but it could be my 20D. I don't mind the weight that many people complain about.

Considering what this lens is meant to do (wide angle to telephoto) this is an outstanding lens. I use this for everything from weddings, portraits, and landscapes. Granted, the focal length isn't ideal on a 1.6x, but this is a great lens if you needed just one lens to get you through low light situations.